Cyclic AMP (cAMP), the prototypical second messenger, regulates a wide variety of cellular processes. In the nervous system, cAMP has a role in many of the medium- to long-term changes that occur in neurons, and that we associate with higher-order functions such as learning and memory. However, it is unclear how one messenger is able to differentially regulate more than 200 cellular targets in response to a large diversity of extracellular stimuli. Until recently methods have not been available to unravel the spatial and temporal complexity of cAMP signals. The long term goals of this project are to measure cAMP signals in neurons and other excitable cells with high spatial and temporal resolution, to elucidate the cellular mechanisms underlying cAMP compartmentation, and to understand how cAMP signals are interpreted by downstream effectors. Several years ago we developed a series of genetically-engineered CNG ion channels as sensors for cAMP near the surface membrane. These channels are opened by the direct binding of cAMP, and allow cations to flow across the membrane. The approach has greater spatial and temporal resolution than other methods for measuring cAMP, and allowed, for the first time, the measurement of distinct cAMP signals within different compartments of non-excitable cells. We now propose to extend this method to excitable cell lines and primary cultured neurons. Aim 1. To understand the molecular events that underlie large and transient cAMP signals near the membrane in excitable pituitary GH4C1 cells. Aim 2. To measure membrane-localized cAMP signals in primary cultured neurons from the rat hippocampus, a brain region known to be important for memory formation.